Mexico City is not far behind. A city that was once one of the most polluted in the world is clearing up thanks to urban agriculture and rooftop gardens.

Gabriela Vargas and Elias Cattan of urban agriculture organization Cultiva Ciudad (Cultivate City), show gardening on the roof of a building in Mexico City, on November 6. A green revolution is sweeping across the car and concrete jungle, the city government has carried out a "green plan" since 2007, but many citizens have also taken it upon themselves to change.